It took a while, but Wizards of the Coast’s corporate masters are finally setting about ruining a perfectly good product. The full scoop is available on that there GR page, featuring an eloquent anonymously-posted comment signed “Ryan Dancey.” The relevant chunk of the revised D20 STL is included below – basically, WotC may deny you the use of the D20 logo if your product doesn’t meet their standards of “decency.”
From the D20 System Trademark License:
4. Quality Standards
The nature of all material You use or distribute that incorporates the Licensed Articles must comply with all applicable laws and regulations, as well as community standards of decency, as further described in the d20 System Guide. You must use Your best efforts to preserve the high standard and goodwill of the Licensed Trademarks. In order to assure the foregoing standard and quality requirements, Wizards of the Coast shall have the right, upon notice to You, to review and inspect all material released by You that uses the Licensed Articles. You shall fully cooperate with Wizards of the Coast to facilitate such review and inspection, including timely provision of copies of all such materials to Wizards of the Coast. Wizards of the Coast may terminate this License immediately upon attempted notice to you if it deems, in its sole discretion, that your use of the Licensed Articles does not meet the above standards.